The present invention relates to a fluorinated diene having two unsaturated bonds, a method for its production and a polymer thereof.
As a fluorinated diene having two carbonxe2x80x94carbon unsaturated double bonds (hereinafter referred to as unsaturated bonds), CF2xe2x95x90CF(CF2)kOCFxe2x95x90CF2 (wherein k is an integer of from 1 to 3) has been known (JP-A-1-14843). By cyclopolymerization of this compound, an amorphous polymer can be obtained, and such a polymer has high elastic modulus, yield and breaking extension and is tough and excellent in impact resistance. Further, its transparency is also high, and it can be used for an optical material such as optical fiber or optical waveguide. However, it has a drawback that when this polymer is used to make an optical material, the glass transition temperature (Tg) is low, and if it is used at a high temperature for a long period of time, the optical properties will change. Accordingly, it has been desired to develop a base material having a higher Tg.
It is an object of the present invention to provide a polymer which maintains the mechanical properties which the above amorphous polymer has, and has a higher glass transition temperature, so that it can be an optical resin material excellent in heat resistance, and to provide a fluorinated diene having two unsaturated bonds, which is capable of presenting such a polymer.
The present invention is the following invention relating to a fluorinated diene represented by the formula 1, a method for its production and a polymer thereof.
A fluorinated diene represented by the formula 1.
A method for producing a fluorinated diene represented by the formula 1, which comprises dehalogenating Z1 and Z2 of a fluorinated compound represented by the formula 2.
A polymer comprising monomer units formed by polymerization of a fluorinated diene represented by the formula 1.
CF2xe2x95x90CF(CF2)nC(CF3)ROCFxe2x95x90CF2xe2x80x83xe2x80x83Formula 1 
CF2Z1CFZ2(CF2)nC(CF3)ROCFxe2x95x90CF2xe2x80x83xe2x80x83Formula 2 
wherein R is a fluorine atom or a trifluoromethyl group, each of Z1 and Z2 which are independent of each other, is a halogen atom other than a fluorine atom, and n is an integer of from 1 to 3.
The fluorinated diene represented by the formula 1 can be obtained by dehalogenating Z1 and Z2 of the fluorinated compound represented by the formula 2. Each of Z1 and Z2 which are independent of each other, is a halogen atom other than a fluorine atom, preferably a chlorine atom or a bromine atom, and particularly preferably, each is a chlorine atom. By the dehalogenation of these halogen atoms, a double bond will be formed, and a fluorinated diene represented by the formula 1 will be formed.
The dehalogenation is carried out by having a dehalogenating agent acted in a polar solvent. The dehalogenating agent is a reaction agent having a function to act on halogen atoms in a substrate thereby to withdraw the halogen atoms. As such a dehalogenating agent, zinc, sodium, magnesium, tin, copper, iron or other metals are preferred. From the viewpoint of such a reaction condition that a relatively low reaction temperature can be employed, zinc is preferred as such a dehalogenating agent. As the polar solvent, an organic polar solvent such as dimethylformamide, 1,4-dioxane, diglyme or methanol, or water, may, for example, be preferably employed.
The molar ratio of the dehalogenating agent to the fluorinated compound represented by the formula 2, is preferably from 1 to 10 times, more preferably from 2 to 3 times. The reaction temperature is usually from 40 to 100xc2x0 C., preferably from 50 to 70xc2x0 C. Usually, the reaction is carried out by dropwise adding the fluorinated compound represented by the formula 2, in the presence of the dehalogenating agent and the solvent, and isolation of the reaction product is carried out by withdrawing the reaction product from the reaction system by distillation promptly after the reaction.
The fluorinated compound represented by the formula 2 is a novel compound, and a compound (formula 2-1) wherein R is a fluorine atom, can be produced, for example, from a known fluorinated compound represented by the formula 3-1. Further, a fluorinated compound (formula 2-2) represented by the formula 2 wherein R is a trifluoromethyl group, can be produced, for example, from a known fluorinated compound represented by the formula 4-1.
CF2Z1CFZ2(CF2)nCF(CF3)OCFxe2x95x90CF2xe2x80x83xe2x80x83Formula 2-1 
CF2Z1CFZ2(CF2)nCFxe2x95x90CF2xe2x80x83xe2x80x83Formula 3-1 
CF2Z1CFZ2(CF2)nC(CF3)2OCFxe2x95x90CF2xe2x80x83xe2x80x83Formula 2-2 
CF2Z1CFZ2(CF2)nCOFxe2x80x83xe2x80x83Formula 4-1 
Firstly, a method for producing the fluorinated compound represented by the formula 2-1 will be described. The unsaturated group in the fluorinated compound represented by the formula 3-1 is epoxidized to an epoxy compound (formula 3-2), and this epoxy compound is isomerized and converted to a fluorinated ketone compound (formula 3-3). To this fluorinated ketone compound, hexafluoropropylene oxide is added to obtain a fluorinated ether compound (formula 3-4), and then, the fluorinated ether compound is pyrolyzed to obtain a fluorinated compound (formula 2-1) represented by the formula 2 wherein R is a fluorine atom. 
For the production of the epoxy compound (formula 3-2), it is possible to apply a method of employing oxygen as disclosed in xe2x80x9cChemistry of organic fluorine compoundxe2x80x9d, 1962 edition, pp. 168-169, edited by Hudlicky, a method of employing hydrogen peroxide as disclosed in JP-B-44-2963, or a method of employing a hypochlorite aqueous solution in the presence of a phase-transfer catalyst.
Particularly preferred is a method of employing a sodium hypochlorite aqueous solution in the presence of a phase-transfer catalyst.
In the case of the method of employing a hypochlorite aqueous solution, the reaction temperature is at least the melting point of the hypochlorite aqueous solution, usually within a range of from xe2x88x9220 to 60xc2x0 C., preferably from xe2x88x9220 to 30xc2x0 C., although it may vary depending upon the phase-transfer catalyst to be used or its amount. The amount of the phase-transfer catalyst is preferably from 0.01 to 20 mass %, particularly preferably from 0.05 to 10 mass %, based on the compound represented by the formula 3-1. As the hypochlorite, an alkali metal salt or an alkaline earth metal salt, such as NaClO, KClO, Ca(ClO)2 or NaBrO, may be mentioned. From the industrial viewpoint, use of NaClO is preferred. The effective concentration of the hypochlorite in the hypochlorite aqueous solution is preferably from 1 to 20 mass %.
As the phase-transfer catalyst, a quaternary ammonium salt, a quaternary phosphonium salt, a quaternary arsonium salt, a sulfonium salt or a crown ether, known as a phase-transfer catalyst, may, for example, be used. Among them, a quaternary ammonium salt and a quaternary phosphonium salt are preferred. As an organic group to be bonded to the nitrogen atom or the phosphorous atom, an alkyl group, an aryl group or an aralkyl group may, for example, be preferred, and as an anion, a halogen ion such as a chlorine ion, or a mineral acid ion such as a sulfate ion, is preferred. A particularly preferred phase-transfer catalyst is a tetraalkylammonium salt.
The epoxy compound (formula 3-2) is subjected to an isomerization reaction in a gas phase or in a liquid phase using a metal compound such as a metal oxide, a metal oxyhalide or a metal halide as a catalyst, whereby a fluorinated ketone compound (formula 3-3) can be obtained. As the metal component of the catalyst, Al, Zr, Ti, Fe, Co, Ni or Cr may, for example, be mentioned, and particularly preferred is aluminum. A reaction wherein a fluorinated epoxide is isomerized in the presence of a catalyst such as aluminum oxide or aluminum chloride to obtain a fluorinated ketone, is known and is disclosed, for example, in U.S. Pat. No. 3,391,119.
In the present invention, when the above isomerization reaction is carried out in a gas phase, a metal oxide catalyst such as xcex3-alumina can be used as the catalyst. However, a more preferred catalyst is a metal oxyhalide. For example, a metal oxyhalide obtainable by activating the above-mentioned metal oxide or multiple metal oxide with a fluorocarbon, is preferred. As the fluorocarbon, a chlorofluorocarbon such as trichlorotrifluoroethane, chlorodifluoromethane, trichlorofluorometane or dichlorodifluoromethane, may, for example, be mentioned.
The isomerization reaction in the gas phase method is carried out by contacting a gas of the epoxy compound (formula 3-2) to the above-mentioned catalyst. The gas of the epoxy compound may be used for the reaction as diluted with an inert gas such as nitrogen gas. The reaction temperature is preferably at least a temperature at which the epoxy compound is vaporized, particularly from 100 to 300xc2x0 C.
In the present invention, when the above-mentioned isomerization reaction is carried out in a liquid phase, the above-mentioned metal oxyhalide or the above-mentioned metal halide can be used as the catalyst. The metal halide is preferably one activated by the fluorocarbon in the same manner as mentioned above. As the solvent, an inert solvent such as a fluorinated solvent, an ether type solvent or an aprotic polar solvent. It is also possible to use as a solvent the liquid fluorocarbon employed for activating the catalyst, as it is. The amount of the catalyst is preferably from 0.005 to 20 mol %, particularly preferably from 0.1 to 10 mol %, based on the epoxy compound (formula 3-2). The reaction temperature is preferably from xe2x88x9220 to +150xc2x0 C., particularly preferably from 20 to 40xc2x0 C.
Further, as the above-mentioned ether type solvent, diethyl ether, methyl tert-butyl ether, dimethoxy ethane, tetrahydrofuran, dioxane, monoglyme, diglyme, triglyme or tetraglyme, may, for example, be mentioned. As the above-mentioned aprotic polar solvent, acetonitrile, benzonitrile, sulfolane, dimethylacetamide or dimethylsulfoxide, may, for example, be mentioned. These solvents may also be used as the ether type solvent or the aprotic polar solvent which will appear in the following description.
In a solvent, a metal fluoride is acted on the fluorinated ketone compound (formula 3-3), followed by a reaction with hexafluoropropylene oxide to obtain a fluorinated ether compound (formula 3-4). The reaction temperature is preferably at most 50xc2x0 C., particularly preferably from 5 to 25xc2x0 C. As the metal fluoride, potassium fluoride, cesium fluoride or sodium fluoride, may, for example, be mentioned. As the solvent for the reaction, an ether type solvent or an aprotic polar solvent is preferred. The reaction pressure of hexafluoropropylene oxide is suitably from 0 to 1 MPa, and preferably, a pressure of from 0.1 to 0.5 MPa is used.
The fluorinated ether compound (formula 3-4) is pyrolized to obtain a fluorinated compound (formula 2-1) of the formula 2 wherein R is a fluorine atom. The pyrolysis may, of course, be carried out by directly pyrolizing the fluorinated ether compound, or the fluorinated ether compound may firstly be converted to an alkali salt of the corresponding carboxylic acid and then hydrolyzed. Further, the fluorinated ether compound (formula 3-4) has an active group (xe2x80x94COF), and after converting such an active group to a group stable in handling, it may be converted to the alkali salt of the carboxylic acid. For example, it may be reacted with an alkanol to form an alkyl ester of the corresponding carboxylic acid, which is then converted to the alkali salt.
In a case where the fluorinated ether compound is directly pyrolized, it is preferred that the fluorinated ether compound is gasified and, if necessary, diluted with an inert gas such as nitrogen gas, followed by contacting it with a solid basic salt or glass beads at a high temperature. The temperature for the pyrolysis is preferably from 200 to 500xc2x0 C., particularly preferably from 250 to 350xc2x0 C. As the solid basic salt, sodium carbonate, potassium carbonate or sodium phosphate may, for example, be used, and particularly preferred is sodium carbonate.
The fluorinated ether compound (formula 3-4) may be reacted with an alkali metal hydroxide to form an alkali metal salt of the corresponding carboxylic acid. This alkali metal salt may be pyrolized at from 100 to 300xc2x0 C., preferably from 150 to 250xc2x0 C. to obtain the desired fluorinated compound. It is preferred to use this alkali metal salt pyrolytic method, since as compared with the above-mentioned gas phase pyrolytic method, the pyrolysis can be carried out at a low temperature, and the yield is also high. Further, it is preferred that the production of the alkali metal salt is carried out by using water or an alcohol as the solvent, and the obtained alkali metal salt is pyrolyzed after being sufficiently dried. Further, as the alkali metal salt, a sodium salt or a potassium salt may be mentioned, but a potassium salt is preferred since the pyrolysis can be carried out at a lower temperature.
Now, a method for producing the fluorinated compound (formula 2-2) from the fluorinated compound represented by the formula 4-1, will be described. Two trifluoromethyl groups are introduced to the carbon atom of a carbonyl group of the fluorinated compound represented by the formula 4-1 to obtain a fluorinated alcohol (formula 4-2), and to this fluorinated alcohol, hexafluoropropylene oxide is added to obtain a fluorinated ether compound (formula 4-3), and then, this fluorinated ether compound is pyrolyzed to obtain the fluorinated compound represented by the formula 2-2.
CF2Z1CFZ2(CF2)nxe2x80x94COFxe2x80x83xe2x80x83Formula 4-1
As a method for introducing two trifluoromethyl groups to the carbon atom of the carbonyl group of the fluorinated compound represented by the formula 4-1, a method of reacting trifluoromethyl trimethylsilane to the fluorinated compound represented by the formula 4-1 in a polar solvent in the presence of a metal fluoride or an ammonium fluoride salt, is preferred. As the metal fluoride, an alkali metal fluoride such as potassium fluoride, cesium fluoride or sodium fluoride, is preferred. Further, as the ammonium fluoride salt, tetrabutylammonium fluoride is preferred. The amount of the metal fluoride or the ammonium fluoride salt to the fluorinated compound represented by the formula 4-1 is preferably from 2 to 3 times by mol, and the amount of trifluoromethyl trimethylsilane to the fluorinated compound represented by the formula 4-1 is preferably from 2 to 2.5 times by mol. The temperature for the reaction is suitably at most 30xc2x0 C., preferably from xe2x88x9278 to +15xc2x0 C. As the polar solvent, the above-mentioned ether type solvent or the aprotic solvent may be mentioned, and particularly preferred is tetrahydrofuran or acetonitrile.
By the above-mentioned reaction employing the metal fluoride, a metal alkoxide of the fluorinated alcohol (formula 4-2) is obtained. This alkoxide is treated with an acid to obtain a fluorinated alcohol. As such an acid, concentrated sulfuric acid, diluted sulfuric acid, concentrated hydrochloric acid or diluted hydrochloric acid may, for example, be preferably employed. Further, this metal alkoxide may be supplied for the subsequent reaction without converting it to the fluorinated alcohol. Namely, the subsequent hexafluropropylene oxide addition reaction may be carried out after converting the fluorinated alcohol to a metal alkoxide, and accordingly, such metal alkoxide may be employed as it is.
In a case where hexafluoropropylene oxide is added to the fluorinated alcohol (formula 4-2) to produce the fluorinated ether compound (formula 4-3), it is usual that the fluorinated alcohol is converted to a metal alkoxide, which is then reacted with hexafluoropropylene oxide. As the metal component of this metal alkoxide, an alkali metal or silver may, for example, be used. For example, in a solvent for reaction, the fluorinated alcohol is reacted with a basic alkali metal salt (such as potassium carbonate or sodium carbonate) at room temperature to obtain a metal alkoxide. Then, the obtained metal alkoxide is reacted with hexafluoropropylene oxide, without isolating it from the solvent for reaction or after isolating it and adding a new solvent for reaction. As the conditions for reacting hexafluoropropylene oxide, the same reaction conditions as in the case where hexafluoropropylene oxide is added to the above-mentioned fluorinated ketone compound (formula 3-3) to produce the fluorinated ether compound (formula 3-4), may be employed.
The pyrolysis of the fluorinated ether compound (formula 4-3) may be carried-out by the same method under the same reaction conditions as the pyrolysis of the above-mentioned fluorinated ether compound (formula 3-4). For example, it is possible to employ a method of pyrolyzing the fluorinated ether compound (formula 4-3) in a gas phase as mentioned above, or a method of converting the fluorinated ether compound (formula 4-3) to a salt of a carboxylic acid as mentioned above, followed by pyrolysis. It is also possible that as mentioned above, the fluorinated ether compound (formula 4-3) is converted to an alkyl ester of the corresponding carboxylic acid, which is then converted to a salt of the carboxylic acid, and this salt of the carboxylic acid is pyrolyzed.
The fluorinated diene represented by the formula 1 of the present invention, is polymerizable and is useful as a monomer for the production of a fluoropolymer. Such a fluorinated diene undergoes cyclopolymerization by an action of a radical polymerization initiator to form a polymer having monomer units having fluorinated alicyclic structures in its main chain. Further, it can be copolymerized with other monomers.
The copolymerizable other monomers are not particularly limited so long as they are radical polymerizable monomers, and a wide range of fluoromonomers, hydrocarbon monomers and other monomers, may be mentioned. Particularly preferred is an olefin such as ethylene, or a fluoroolefin such as tetrafluoroethylene. Further, a fluorinated vinyl ether type monomer such as a perfluoro(alkyl vinyl ether), a cyclopolymerizable fluorinated diene (other than the fluorinated diene represented by the formula 1) such as perfluoro(butenyl vinyl ether) or perfluoro(allyl vinyl ether) or a monomer having a fluorinated alicyclic structure such as perfluoro(2,2-dimethyl-1,3-dioxole), may, for example, be also copolymerizable. Such other monomers may be copolymerized with the fluorinated diene, alone or in combination of two or more of them.
The present invention also provides a homopolymer of the above-mentioned fluorinated diene of the present invention, or a copolymer of two or more of such fluorinated dienes, and a copolymer of the above-mentioned fluorinated diene of the present invention with other monomers copolymerizable therewith. The proportion of monomer units formed by polymerization of the fluorinated diene of the present invention in such polymers, is preferably from 30 to 100 mol %, particularly preferably from 50 to 100 mol %, based on the total monomer units. Further, the molecular weight is preferably from 500 to 100,000, particularly preferably from 500 to 10,000.
As the radical polymerization initiator, any polymerization initiator employed in usual radical polymerization, such as an azo compound, an organic peroxide or an inorganic peroxide, may be used. The following compounds may be mentioned as specific radical polymerization initiators. Diisopropyl peroxydicarbonate, an azo compound such as 2,2xe2x80x2-azobis(2-amidinopropane) dihydrochloride, 4,4xe2x80x2-azobis(4-cyanopentanoic acid), 2,2xe2x80x2-azobis(4-methoxy-2,4-dimethylvaleronitrile) or 1,1xe2x80x2-azobis(1-cyclohexane carbonitrile), an organic peroxide such as benzoyl peroxide, perfluoro benzoyl peroxide, perfluorononanoyl peroxide or methyl ethyl ketone peroxide, and an inorganic peroxide such as K2S2O8 or (NH4)2S2O8.
The method for polymerization is also not particularly limited, and it may, for example, be so-called bulk polymerization wherein the fluorinated diene is directly subjected to polymerization, a solution polymerization which is carried out in a fluorohydrocarbon, a chlorinated hydrocarbon, a chlorinated fluorohydrocarbon, an alcohol, a hydrocarbon or other organic solvent, which is capable of dissolving the fluorinated diene, suspension polymerization which is carried out in an aqueous medium in the presence or absence of a suitable organic solvent, or emulsion polymerization which is carried out in an aqueous medium in the presence of an emulsifier. The temperature and the pressure for the polymerization are not particularly limited, but preferably suitably set taking into consideration various factors such as the boiling point of the fluorinated diene, the required heating source and removal of polymerization heat. For example, the polymerization temperature may be set at a suitable temperature within a range of from 0 to 200xc2x0 C., particularly preferably from 30 to 100xc2x0 C. Further, with respect to the polymerization pressure, the polymerization may be carried out under reduced pressure or elevated pressure, and practically, it can be carried out suitably at a level of from normal pressure to 10 MPa, further specifically from normal pressure to 5 MPa.
As characteristics of the polymer of the present invention, it may be mentioned that it is excellent in transparency, it has high elastic modulus, yield and breaking elongation and is tough and excellent in impact resistance, and it has a high glass transition temperature and high heat resistance. By virtue of such characteristics, the polymer of the present invention can be utilized as an optical resin material to be used for optical fiber, optical waveguide or optical transmitter such as a lens, which is excellent in heat resistance by itself. Further, the polymer of the present invention is characterized also in that it is optically transparent and has a refractive index lower than the conventional transparent fluororesin. For this reason, it may be combined with e.g. a conventional transparent fluororesin having a low refractive index, such as CYTOP (trade name, manufactured by Asahi Glass Company, Limited) or Teflon AF (trade name, manufactured by Dupont) to obtain an optical device such as optical fiber or optical waveguide excellent in optical transparency and having high performance.
Especially, a plastic optical fiber wherein a mixture having a refractive index raising agent mixed to the polymer of the present invention, is used as a core, and the polymer of the present invention is used as a clad, is excellent in heat resistance. Such plastic optical fiber may be of a step index type or a refractive index distribution type. The polymer of the present invention may suitably be employed for either type, but particularly suitable for a refractive index distribution type plastic optical fiber. As the above-mentioned refractive index raising agent, a fluorinated low molecular weight compound is preferred, since the transparency of the resulting mixture is thereby excellent. As such a fluorinated low molecular weight compound, perfluoro(triphenyltriazine), perfluoro(1,3,5-triphenylbenzene) or chlorotrifluoroethylene oligomer, may, for example, be mentioned as a preferred example. Further, a mixture of two or more of such compounds may be used as the refractive index raising agent.
The following methods may be mentioned as methods for producing the above-mentioned refractive index distribution type plastic optical fiber. A method wherein a cylindrical columnar molded product of the polymer of the present invention is produced wherein at the center axis portion a prescribed concentration of a refractive index raising agent is present, and the refractive index raising agent is diffused by thermodiffusion from the center axis portion in a radial direction to form a refractive index distribution, and then, the obtained cylindrical columnar molded product is used as a preform to form an optical fiber (JP-A-8-5848). A method wherein the polymer of the present invention is melt-extruded and formed into a fiber shape to form an optical fiber, whereby a highly concentrated refractive index raising agent is permitted to be present at the center axis portion, and the optical fiber is produced while thermally diffusing the refractive index raising agent (JP-A-8-5848). A method wherein a cylindrical tubular molded product is made of the polymer of the present invention, a predetermined amount of a refractive index raising agent is introduced to the center portion, followed by thermodiffusion to form a cylindrical tubular preform having a refractive index distribution, from which an optical fiber is formed (JP-A-8-334633).
Further, the polymer of the present invention is soluble in a fluorinated solvent such as perfluoro(2-butyltetrahydrofuran), perfluorooctane, perfluorohexane, perfluoro(tributylamine), perfluoro(tripropylamine), perfluorobenzene or dichloropentafluoropropane. A solution obtained by dissolving the polymer of the present invention in such a solvent, may be coated on a substrate such as a glass or a silicon wafer by spin coating or spraying, and then the solvent is evaporated and dried to form a thin film.
Further, with the polymer of the present invention, the terminal group may readily be substituted by e.g. heat treatment or fluorine gas treatment, and the adhesive property to various substrates may be modified by a treating method. For example, the polymer of the present invention may be heated at a temperature of at least 200xc2x0 C. in the presence of air and then treated in water to introduce a carboxyl group to the terminal. Further, it may be reacted with fluorine gas to remove the terminal reactive functional group, whereby the thermal stability of the polymer can be improved.